Datasheet MC1489, MC1489A (ON Semiconductor) - 6

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MC1489, MC1489A APPLICATIONS INFORMATION General Information
The Electronic Industries Association (EIA) has released turn−on voltage of 1.25 V and turn−off of 1.0 V for a typical the EIA−232D specification detailing the requirements for hysteresis of 250 mV. The MC1489A has typical turn−on of the interface between data processing equipment and data 1.95 V and turn−off of 0.8 V for typically 1.15 V of communications equipment. This standard specifies not hysteresis. only the number and type of interface leads, but also the Each receiver section has an external response control voltage levels to be used. The MC1488 quad driver and its node in addition to the input and output pins, thereby companion circuit, the MC1489 quad receiver, provide a allowing the designer to vary the input threshold voltage complete interface system between DTL or TTL logic levels levels. A resistor can be connected between this node and an and the EIA−232D defined levels. The EIA−232D external power supply. Figures 4, 6 and 7 illustrate the input requirements as applied to receivers are discussed herein. threshold voltage shift possible through this technique. The required input impedance is defined as between This response node can also be used for the filtering of 3000 W and 7000 W for input voltages between 3.0 and 25 V high frequency, high energy noise pulses. Figures 10 and 11 in magnitude; and any voltage on the receiver input in an show typical noise pulse rejection for external capacitors of open circuit condition must be less than 2.0 V in magnitude. various sizes. The MC1489 circuits meet these requirements with a These two operations on the response node can be maximum open circuit voltage of one VBE. combined or used individually for many combinations of The receiver shall detect a voltage between − 3.0 and interfacing applications. The MC1489 circuits are −25 V as a Logic “1” and inputs between 3.0 and 25 V as a particularly useful for interfacing between MOS circuits and Logic “0.” On some interchange leads, an open circuit of DTL/TTL logic systems. In this application, the input power “OFF” condition (300 W or more to ground) shall be threshold voltages are adjusted (with the appropriate supply decoded as an “OFF” condition or Logic “1.” For this and resistor values) to fall in the center of the MOS voltage reason, the input hysteresis thresholds of the MC1489 logic levels (see Figure 12). circuits are all above ground. Thus an open or grounded The response node may also be used as the receiver input input will cause the same output as a negative or Logic “1” as long as the designer realizes that he may not drive this input. node with a low impedance source to a voltage greater than one diode above ground or less than one diode below
Device Characteristics
ground. This feature is demonstrated in Figure 13 where two The MC1489 interface receivers have internal feedback receivers are slaved to the same line that must still meet the from the second stage to the input stage providing input EIA−232D impedance requirement. hysteresis for noise rejection. The MC1489 input has typical 6 6
MC1489 MC1489A
5 5 10 pF 100 pF 300 pF 500 pF 12 pF 100 pF 300 pF 500 pF 4 4 AMPLITUDE (V) 3 AMPLITUDE (V) 3 in in E , E , 2 2 1 1 10 100 1000 10,000 10 100 1000 10,000 PW, INPUT PULSE WIDTH (ns) PW, INPUT PULSE WIDTH (ns)
Figure 10. Typical Turn On Threshold versus Figure 11. Typical Turn On Threshold versus Capacitance from Response Control Pin to GND Capacitance from Response Control Pin to GND http://onsemi.com 6